Energy & Power · Study deck

Energy-Aware Case Studies

Picture two field sensors with the same battery where one lasts twice as long.

Battery Bruno is your guide for this deck.

awarecasestudies
Battery Bruno, the module guide, in a scene from this chapter.
iotclass.org

After studying this chapter

Learning objectives

You will be able to:

  • Explain: A case study is useful when it tells you what was measured, what was assumed, and what changed after deployment.
  • Explain: Initial symptom: Firmware entered deep sleep correctly, but whole-board sleep current was far above the estimate.
  • Explain: Transferable pattern: When a field sensor fails a battery target, first inspect the full-period trace.
  • Explain: That point is the next premise in the cell discharges even when the sensor sleeps.
iotclass.org

Major section

Start With the Evidence Record

Duty cycle means the share of time a device spends in an active state.

  • This check explains selected workloads and conditions, not every deployment.
  • The deeper cases examine trade-offs, measurement limits, maintenance, and transferable lessons.
  • A case study is useful when it tells you what was measured, what was assumed, and what changed after deployment.
iotclass.org

Major section

Case Study 1: Field Soil Sensor

Shorter connection window and fewer reports.

  • The dominant cost was not the soil measurement.
  • If Baseline cannot be connected to: After revision, the surrounding conclusion is premature.
  • Transferable pattern: When a field sensor fails a battery target, first inspect the full-period trace.
Before-and-after field soil sensor ledger: measurement interval, sleep state, radio behavior, and the review lesson move from a high-current idle loop and full reconnects to deep sleep, a shorter active window, and batched reporting.
Before-and-after field soil sensor ledger: measurement interval, sleep state, radio behavior, and the review lesson move from a high-current idle loop and full reconnects to deep sleep, a shorter active window, and batched reporting.
iotclass.org

Major section

Case Study 4: Board Leakage Failure

Initial symptom: Firmware entered deep sleep correctly, but whole-board sleep current was far above the estimate.

  • The MCU was not the problem; support circuitry stayed powered.
  • Regulator current: The regulator quiescent current was larger than the MCU sleep current.
  • Transferable pattern: A low-power MCU does not make a low-power product.
iotclass.org

Major section

Pattern Map

Current trace shows a real low-current sleep floor and bounded wake window.

  • Upload size, attach time, retries, signal quality, and batching behavior are measured.
  • Accuracy, freshness, missed events, and sensor warm-up are checked.
  • Whole-board sleep current is measured after debug and peripheral shutdown.
Energy case-study pattern map connecting the field soil sensor, asset tracker, vibration monitor, and board leakage cases to reusable review lessons: duty-cycle, communication, sensing, and board repair.
Energy case-study pattern map connecting the field soil sensor, asset tracker, vibration monitor, and board leakage cases to reusable review lessons: duty-cycle, communication, sensing, and board repair.
iotclass.org

Major section

The Cell Discharges Even When The Sensor Sleeps

Its Baseline and ledger labels identify the conditions that must be checked together.

  • That point is the next premise in the cell discharges even when the sensor sleeps.
Use the same evidence chain for battery-chemistry case studies: measure the baseline, identify the dominant drain, change one lever, re-measure under the same boundary, check service impact, and transfer only the lesson.
Use the same evidence chain for battery-chemistry case studies: measure the baseline, identify the dominant drain, change one lever, re-measure under the same boundary, check service impact, and transfer only the lesson.
iotclass.org

Deck summary

Key takeaways

Duty cycle means the share of time a device spends in an active state.

  • Shorter connection window and fewer reports.
  • Initial symptom: Firmware entered deep sleep correctly, but whole-board sleep current was far above the estimate.
  • Current trace shows a real low-current sleep floor and bounded wake window.
  • Its Baseline and ledger labels identify the conditions that must be checked together.
iotclass.org

Retrieval practice

Recall check 1 of 6

Battery Bruno says: answer from memory, then check your reasoning.

Q1A case study claims multi-year battery life after changing protocols, but provides no current trace, retry count, or payload size. What is the strongest review response?

AAccept it because the new protocol shortens airtime
BAsk for matched before-and-after energy ledgers
CReject it because sensor warm-up may cost more
DUse the claimed lifetime as the battery-life estimate for your own product
Show answer

Answer: B A credible energy case study exposes the same evidence boundary before and after the change: payload, timing, retries, sleep current, and service result.

iotclass.org

Retrieval practice

Recall check 2 of 6

Battery Bruno says: answer from memory, then check your reasoning.

Q2A vibration monitor saves energy by extracting features locally before upload. Which lesson is safest to transfer to a new design?

AAlways process every workload locally
BAlways stream raw data to preserve accuracy
CCompare compute energy with saved radio energy
DSwitch every sensor to the same feature-extraction algorithm
Show answer

Answer: C A case-study lesson transfers when the underlying evidence pattern matches: data size, compute cost, service requirement, and measurement boundary.

iotclass.org

Retrieval practice

Recall check 3 of 6

Battery Bruno says: answer from memory, then check your reasoning.

Q3Place each case-study record where it lives so you can separate measured evidence from a targeted fix and a transferable service result.

ABaseline trace
BMarketing quote
CCourse footer
DTheme switcher
Show answer

Answer: A Follow measure, change, and transfer so you can tell a demonstrated energy improvement from an attractive but unproven claim.

iotclass.org

Retrieval practice

Recall check 4 of 6

Battery Bruno says: answer from memory, then check your reasoning.

Q4A soil sensor must run unattended for 10 years drawing an average of about 15 uA. Why is a standard Li-ion cell a poor chemistry choice here, even at a generous capacity?

ALi-ion self-discharge acts like a large parallel leak.
BLi-ion has too little energy density for a small sensor.
CLi-ion voltage is too low to power a sensor.
DLi-ion cannot be used below room temperature at all.
Show answer

Answer: A On a 2000 mAh cell, 2%/month is about 40 mAh/month, an equivalent leak near 55 uA - several times the 15 uA load.

iotclass.org

Retrieval practice

Recall check 5 of 6

Battery Bruno says: answer from memory, then check your reasoning.

Q5A 2000 mAh Li-ion cell self-discharges at about 2% per month. Modeled as a constant parallel leak, what equivalent current does that represent?

AAbout 55 uA.
BAbout 3 uA, the same as a low-self-discharge lithium primary cell.
CAbout 40 mA, taking 40 mAh as if it were a current.
DZero, because self-discharge only matters while the device is off.
Show answer

Answer: A 2% of 2000 mAh is 40 mAh lost per month; dividing by about 730 hours gives 0.055 mA, or 55 uA.

iotclass.org

Retrieval practice

Recall check 6 of 6

Battery Bruno says: answer from memory, then check your reasoning.

Q6A design budgets a Li-SOCl2 self-discharge equivalent of 3 uA measured at 20 C, but the sensor is sealed in a dark enclosure that runs near 40 C in summer. What is the most defensible correction to the self-discharge budget?

ARaise the estimate for the hotter enclosure.
BLower the self-discharge estimate, because heat makes chemical reactions slower.
CLeave it at 3 uA, because self-discharge does not depend on temperature.
DSwitch to Li-ion, which is immune to temperature effects.
Show answer

Answer: A A 20 C to 40 C rise spans two 10 C steps, so the equivalent leak can be on the order of four times the bench figure.

iotclass.org

Print reference

Answers 1 of 2

Answer key.

  1. B · A credible energy case study exposes the same evidence boundary before and after the change: payload, timing, retries, sleep current, and service result.
  2. C · A case-study lesson transfers when the underlying evidence pattern matches: data size, compute cost, service requirement, and measurement boundary.
  3. A · Follow measure, change, and transfer so you can tell a demonstrated energy improvement from an attractive but unproven claim.
iotclass.org

Print reference

Answers 2 of 2

Answer key.

  1. A · On a 2000 mAh cell, 2%/month is about 40 mAh/month, an equivalent leak near 55 uA - several times the 15 uA load.
  2. A · 2% of 2000 mAh is 40 mAh lost per month; dividing by about 730 hours gives 0.055 mA, or 55 uA.
  3. A · A 20 C to 40 C rise spans two 10 C steps, so the equivalent leak can be on the order of four times the bench figure.
iotclass.org